I am running the iOS 10 Beta on my Verizon iPhone 6S Plus 64GB RG and I am noticing that when I am in the All Inbox view and I tap Edit and then Mark All As Read the blue unread dots are not immediately going away like in previous iOS itterations. Anybody else having this issue?
mail in iOS 10 Beta 1
I have the same phone as you, allbeit in Space Gray, but I was able to test this using an Exchange account, and the dots all disappeared immediately.
Weak service area? Exchange email? File a bug either way 🙂